KVM: VMX: Inject #GP on ENCLS if vCPU has paging disabled (CR0.PG==0)

Inject a #GP when emulating/forwarding a valid ENCLS leaf if the vCPU has
paging disabled, e.g. if KVM is intercepting ECREATE to enforce additional
restrictions.  The pseudocode in the SDM lists all #GP triggers, including
CR0.PG=0, as being checked after the ENLCS-exiting checks, i.e. the
VM-Exit will occur before the CPU performs the CR0.PG check.

Fixes: 70210c0 ("KVM: VMX: Add SGX ENCLS[ECREATE] handler to enforce CPUID restrictions")
Cc: Binbin Wu <binbin.wu@linux.intel.com>
Cc: Kai Huang <kai.huang@intel.com>
Tested-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20230405234556.696927-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/x86/kvm/vmx/sgx.c

@@ -382,7 +382,7 @@ int handle_encls(struct kvm_vcpu *vcpu)
 
 	if (!encls_leaf_enabled_in_guest(vcpu, leaf)) {
 		kvm_queue_exception(vcpu, UD_VECTOR);
-	} else if (!sgx_enabled_in_guest_bios(vcpu)) {
+	} else if (!sgx_enabled_in_guest_bios(vcpu) || !is_paging(vcpu)) {
 		kvm_inject_gp(vcpu, 0);
 	} else {
 		if (leaf == ECREATE)